The present invention generally relates to plastic containers. The present invention also relates to retortable containers.
As is known, containers and their contents are commonly subjected to retort conditions for sterilization. However, during a retort process, when a plastic container is subjected to relatively high temperatures and pressures, the plastic container""s shape will distort. Upon cooling, the plastic container generally retains this distorted shape or at least fails to return to its pre-retort shape. In a worst case, the plastic container experiences a catastrophic failure, resulting in a collapse or a xe2x80x9cblow outxe2x80x9d of a portion of the plastic container.
One solution to overcoming these known disadvantages may be to provide a plastic container having very thick walls. The thicker walls might assist in resisting the high internal pressure generated within the plastic container. While this solution might resist some internal pressure, it often does not provide enough resistance to provide for higher value internal pressures. Thus, the plastic container often still experiences catastrophic failures under this proposed solution. Further, the increased wall thickness unfavorably increases the cost of the plastic container.
Another solution to overcoming the known disadvantages is to provide a plastic container having a flexible bottom portion. The flexible bottom portion of the proposed plastic container expands to accommodate the increased internal pressure of the plastic container. This solution is described in U.S. Pat. No. 5,217,737.
Accordingly, there is a need to provide a retortable plastic container that has a minimum weight and that has a flexibility to substantially return to its original shape after being subjected to a retort process.
The present disclosure provides one or more inventions directed to improvements in retortable plastic containers. These improvements can be practiced jointly or separately.
To this end, in an embodiment, there is provided a retortable plastic container, comprising a side wall having at least one flexing portion extending from a top horizontal line around a circumference of the side wall to a bottom horizontal line around the circumference of the side wall. The flexing portion has an inwardly directed surface relative to the circumference of the side wall. The inwardly directed surface has a first length measured along the inwardly directed surface, in a central vertical plane from the top horizontal line to the bottom horizontal line, which is greater than a straight line distance between the top and bottom horizontal lines in the same vertical plane, and a second length measured along the inwardly directed surface along a perimeter of the flexing portion, in a horizontal plane, which is greater than a circumference of a circle having a radius of an average distance from a central vertical axis of the container to the inwardly directed surface, the circumference of the circle being in the horizontal plane.
In an embodiment, the inwardly directed surface includes a plurality of inwardly recessed indentations.
In another embodiment, the inwardly directed surface includes a plurality of ribs. The ribs each comprise a recessed portion being recessed toward an interior of the plastic container. The recessed portion resiliently flexes in a direction of an exterior of the container during retort. The ribs can be substantially aligned in the direction of the height of the container or a direction skewed to the direction of the height of the container.
In an embodiment, the inwardly directed surface includes a plurality of inwardly recessed dimples.
In an embodiment, the inwardly directed surface includes an array of connected geometric shapes.
In an embodiment, the side wall further has a plurality of flexing portions each at a different position along the height of the plastic container.
In an embodiment, the retortable plastic container further has a bottom portion, wherein at least a region of the bottom portion can resiliently flex in a direction of an exterior of the plastic container during retort. Alternatively, the bottom portion can have a sufficient thickness to not flex during retort. As discussed below, the bottom portion of the plastic container does not need to flex in order for the plastic container to assume a merchantable shape after a retort process.
In an embodiment, the side wall has a thickened portion proximate the flexing portion, the thickened portion having a thickness greater than a thickness of regions of the side wall adjacent the thickened portion.
In an embodiment, the side wall has an inwardly depressed groove formed therein about at least a part of the circumference of the side wall.
In an embodiment, the plastic container comprises polypropylene. In another embodiment, the plastic container comprises multi-layered polypropylene.
The plastic container can be used with a variety of products, such as, for example, aqueous products and/or comestibles.
There is also provided, in an embodiment, a retortable plastic container, comprising first and second longitudinal ends; a wall extending between the ends and surrounding a longitudinal axis; and flexible wall members positioned about a circumference of the wall, the flexible wall members being concavities in the wall and being effective to flex outwardly from the plastic container during retort in response to increased internal plastic container pressure and to return to a merchantable shape upon cessation of retort in response to decreased internal plastic container pressure.
There is also provided, in an embodiment, a method of forming a retortable plastic container, the method comprising forming a side wall having at least one flexing portion extending from a top horizontal line around a circumference of the side wall to a bottom horizontal line around the circumference of the side wall, the flexing portion having an inwardly directed surface relative to the circumference of the side wall, the inwardly directed surface having a first length measured along the inwardly directed surface, in a central vertical plane from the top horizontal line to the bottom horizontal line, which is greater than a straight line distance between the top and bottom horizontal lines in the same vertical plane, and a second length measured along the inwardly directed surface along a perimeter of the flexing portion, in a horizontal plane, which is greater than a circumference of a circle having a radius of an average distance from a central vertical axis of the container to the inwardly directed surface, the circumference of the circle being in the horizontal plane.
In an embodiment, the side wall is formed with a plurality of flexing portions each at a different position along the height of the plastic container.
In an embodiment, a bottom portion of the plastic container is formed. At least a region of the bottom portion resiliently flexes in a direction of an exterior of the container during retort.
In an embodiment, the side wall is formed with a thickened portion proximate the flexing portion, the thickened portion having a thickness greater than a thickness of regions of the side wall adjacent the thickened portion.
In an embodiment, the side wall is formed with an inwardly depressed groove therein about at least a part of the circumference of the side wall.
There is further provided, in an embodiment, a method of reducing differential pressure on a plastic container during retort, the method comprising: providing a side wall of the plastic container, the side wall having at least one flexing portion extending from a top horizontal line around a circumference of the side wall to a bottom horizontal line around the circumference of the side wall, the flexing portion having an inwardly directed surface relative to the circumference of the side wall, the inwardly directed surface having: a first length measured along the inwardly directed surface, in a central vertical plane from the top horizontal line to the bottom horizontal line, which is greater than a straight line distance between the top and bottom horizontal lines in the same vertical plane, and a second length measured along the inwardly directed surface along a perimeter of the flexing portion, in a horizontal plane, which is greater than a circumference of a circle having a radius of an average distance from a central vertical axis of the container to the inwardly directed surface, the circumference of the circle being in the horizontal plane.
These and other features of the present invention will become clearer with reference to the following detailed description of the presently preferred embodiments and accompanying drawings.